High speed digital data network equipment must meet international requirements limiting radiated emissions to reduce interference with radio communications systems. For example, in the United States, above 960 MHz, the Federal Communication Commission (FCC) requires unintentional radiators to generate electric fields less than 300 uV/m at a distance of 10 m. As data rates increase, unintentional radiation tends to increase because higher edge rates and symbol rates radiate more efficiently on a given conductor geometry and the fields penetrate through holes in shields more efficiently. Power consumption of leading edge high speed data transceivers is fairly high and is usually cooled with the assistance of air flow, so openings in shielding enclosures are required even though they facilitate unintentional radiation, making it difficult to sufficiently shield emissions.
Furthermore, it is common to incorporate 32 or 48 or more transceiver modules per unit of digital switches and related network equipment. Each transceiver modules may include eight or more transmitters and receivers. Generally speaking, the transceiver modules are distributed along rack mounted equipment approximately 19 inches wide. This configuration represents a tightly-grouped array of (unintentional) radiators which spans many wavelengths.